Method and device for hot gas engine or gas refrigeration machine

ABSTRACT

A closed-cycle gas expansion engine and a closed-cycle or opencycle gas expansion refrigerator, including a thermal regenerator, devices for transferring heat into the gas or subtracting cold gas, and a piston assembly for developing approximately 180* phase difference in the varying volumes of the warmer and colder gas chambers. A general valve mechanism is employed for properly timed flow of working gas into the primary gas chamber from a plenum chamber containing cooling devices for closed-cycle operation, or for flow of working gas into the primary gas chamber from an ambient atmosphere for open-cycle operation. A valve mechanism, separate or coupled to the first mechanism, is used for proper initiation and termination of gas flow between the primary and secondary chambers in one particular phase of the reciprocating piston motion. Still another valve, which may be integrated with any of the other mentioned valve mechanisms, is used for release of suitably recompressed working gas in the secondary chamber into the plenum chamber with a closed cycle, or for properly timed exhaust of such gas back to the ambient atmosphere with an open cycle.

United States Patent Kniiiis [451 Oct. 17, 1972 [54] METHOD AND DEVICEFOR HOT GAS [57] ABSTRACT ENGINE 0R GAS REFRIGERATION A closed-cycle gasexpansion engine and a closed- MACHINE cycle or open-cycle gas expansionrefrigerator, includ- [72] Inventor: Stellan Kniiiis, Fregattvagen 2,ing a thermal regenerator, devices for transferring T b S d heat intothe gas or subtracting cold gas, and a piston assembly for deve opingapproximately 180 phase dif- [22] led: 1971 ference in the varyingvolumes of the warmer and 21 A N 115,547 colder gas chambers. A generalvalve mechanism is employed for properly timed flow of working gas intothe primary gas chamber from a plenum chamber con- [30] ForelgnApphcatlo P'mmy Data taining cooling devices for closed-cycle operation,or March 2, 1970 Sweden ..l2640/70 for flow of Working gas into the P ygas Chamber from an ambient atmosphere for open-cycle opera- 52 us. Cl..60/24, 62/6 tion- A valve mechanism, separate of coupled to the [51]Int. Cl ..F0lk 7/06 first mechanism is used for Proper initiation and[58] Field of Search ..60/24; 62/6 minati gas between the Primary anddary chambers in one particular phase of the l 56] Reierences Citedreciprocating piston motion. Still. another valve, which may beintegrated with any of the other mentioned UNITED STATES PATENTS valvemechanisms, is used for release of suitably recompressed working gas inthe secondary chamber 33 into the plenum chamber with a closed cycle, orfor properly timed exhaust of such gas back to the am- 2,7s4,54s 3/1957Fiala ..60/24 his, atmosphere with an open cycle 3,400,281 9/1968 Malik..60/24 X a 3,460,344 8/1969 Johnson ..60/24 3,552,l20 l/l97l Beale..60/24 Primary Examiner-Martin P. Schwadron Assistant Examiner-A. M.Ostrager Attorney-Sokolski & Wohlgemuth 35 Cla m-S, Draw Eire-" 48 so 36H E AT H/ 46 1T 38 EXCHANGER BURNER 44 PLE NUM 42 C OOLE R 40 HEATTHERMAL v 54 EXCHANGER REGENERATOR 30 2a 5s v 58 2o Q 26PATENTEUUBHTIQTZ 3.698.182

SHEET 2 OF 9 TEMPERATURE E NTROPY (,0)

FIG. 2

COOLER HEAT v 'V EXCHANGER 30b HEAT H EXCHANGER" THERMAL J H REGENERATORTHERMAL 28b REGENE RATOR 28a FIG.5

INMENTOR STELLAN KNOOS somsxl a WOHLGEMUTH ATTORNEYS PAIENTEDnm 17 I9723. 6 98. 18 2 sum 3 or 9 PLENUM COOLER HEAT THERMAL I 56 EXCHANGERREGENERATOR t j as |2 If. .1 l8 I60. I an l6b FIG.4 J 22 FROM AMBIENT TOAIMBIENT REGENERATOR TO EN VOLUME lGb FIG. I I INVENTOR STELLAN KubsSOKOLSKI a WOHLGEMUTH ATTORNEYS PATENTED BT 17 1 3,698,182

saw 1; [1F 9 HEATER FIG. 6

COOLER INVENTOR STELLAN KNds SOKClSKl 8 WOHLGEMUTH ATTORNEYS Pmmmncm me3,698,182

SHEET 6 OF 9 GAS T T EBQM A QJRCE ERQM AMBIENT AMBIENT Amsm VREGENERATOR REGENERATOR V I/Il/l/I/ COLD GAS OUTLET \J M REGENERATORFIG. 10 lNVENTOR STELLAN KNDOS BY soKoLsm & WOHLGEMUTH ATTORNEYSPATENTEI'JIIBI I 1 I972 3 .6 98. 18 2 SHEET 8 OF 9 HEAT EXCHANGERFfEGENERATOR 24 A 24 :I

20s O v M REGENERATOR REGENERATOR l [L 2I4 FIG. I4 I I I TO AMBIENT 1I74 ATMOSPHERE REGEN- /2 FROM ANBIENT ATMOSPHERE I 9 28 mg I86 I REGEN.

L II I,

INVENTOR 224 STELLAN KNbs SOKOLSKI GI WOHLGEMJTH ATTORNEYS PATENTEDHCI 1I912 3.698. 182

SHEET 9 [1F 9 FRQM A I T ATMOSPHERE 28\ T PRIMARY V 56 A THERMAL CHAMBERREGENERATOR FIG. |5b CHAMBER .HEAI 22s EXCHANGER 23o FIG. I56

FIG. 15 I 228 m \THERMAL o REGENERATOR 22a m INVENTOR STELLAN KN66SSJKOLSKI 8| WCHL'GEMUTH ATTORNEYS METHOD AND DEVICE FOR HOT GAS ENGINEOR GAS REFRIGERATION MACHINE BACKGROUND OF THE INVENTION of performingthe desired thermodynamic cycles for the working gas in such devices.

Several arrangements are available for performing the Ericsson and themore well-known Stirling cycle for hot gas engines withexternal-combustion heat addition. The most recent of the Stirlingengines employ two pistons reciprocating in a single cylinderapproximately 90 out of phase with each other. Stirling engines of thiskind are receiving much attention, particularly due to their potentiallylow-pollution exhaust gas emission, but also due to high thermalefficiency and low noise. They further have the advantage of capabilityof use with a great number of different liquid and gaseous fuels. TheStirling engines are necessarily equipped with thermal regenerators inorder to obtain a high thermodynamic efficiency. Characteristic ofpresent Stirling-cycle engines is a requirement of liquid cooling. Theworking gas, which could be helium, hydrogen or less preferred air,rejects heat in a cooler placed in immediate connection with the thermalregenerator inthe gas line between the hot and colder work chambers. Foroptimum efficiency, the dead space of the cooler, as well as regeneratorand heater dead-spaces should be minimum. A compromise generally has tobe made between the cooler deadspace and the efficiency of the cooler,by keeping the dead-space moderately small but allowing the temperaturedifference between the liquid coolant and the working gas to berelatively large, and hence a lower overall temperature ratio and lowerthermodynamic efficiency than could otherwise be attained. Contributingreasons why hot gas engines are not in widespread use today are largeweight and high mechanical complexity of existing designs, and theirestimated high production cost, e.g. as compared to Otto-cycle andDiesel-cycle engines with the same power output. Materials and sealingproblems of the past have to a great extent been solved by moderntechnology, and no large technological barriers exits today to thepractical use of hot gas engines, e.g. for automobile propulsion.However, the use of Stirling engines for automobiles has so far not beenfavored, primarily due to the projected high manufacturing cost of theengine, the relatively poor power/weight ratio, and practicaldifficulties to be experienced in handling high pressure helium andhydrogen working gases, e.g. in service and overhaul. With the moresevere air-pollution problem on hand, the demand of a low-pollutionengine is stronger than ever, and the Stirling engine or hot gas enginesin general could provide the sought for solution if they could be madepracticable.

Modern Stirling engine concepts and associated devices are described,for example, in the following U.S. Pats: No. 3,166,911 to Meijer; No.3,442,079 to Meijer; No. 3,011,306 to Meijer; No. 3,036,427 to Meijer;No. 3,015,475 to Meijer; No. 3,472,037 to Kohler, and No. 3,458,994 toHeffner. Other hot gas engines are described in U.S. Pats. No. 3,183,662to Korsgren, No. 3,460,344 to Johnson, No. 3,407,593 to Kelly, No.3,138,918 to Baker, No. 3,174,276 to Baker, No. 3,385,051 to Kelly, No.3,080,706 to Flynn and No. 2,564,363 to Horwitz. An interestinginvention for a hot gas engine is described in U.S. Pat. No. 3,457,722to Bush, where the cycle is interrupted during idle periods by the useof valves, and heating and cooling coils are connected into the system.Unfortunately, the device appears to be mechanically complex and usesvalves operating in high-temperature environments.

Several gas-expansion refrigerator systems have been devised and builtwith the Stirling thermodynamic cycle. Such gas-expansion refrigeratorsoperate with a closed thermodynamic cycle resembling the engine cycle,with the difference that mechanical work is added to the gas, heattransferred to the gas at a low temperature (the refrigeration load),and heat rejected at a higher temperature. Stirling-cycle refrigeratorshave come into widespread practical use, starting a few decades ago,while the corresponding engine still awaits exploitation. Stirling-cyclerefrigerators are today capable of providing temperatures considerablybelow 100K, and a few systems have demonstrated refrigeration-loadcapabilities much above 10 kW at these temperatures. Measured overallefficiencies for such systems have been as high as 40 percent of theCarnot efficiency (the theoretical limit). Stirling-cycle refrigeratorshave been miniaturized and used for cooling, e.g., electro-opticaldevices. Temperatures below 20K in multiple-step operation have beendemonstrated with helium as the working gas. The refrigeration-loadcapabilities for these devices have been typically of the order of 1watt, with the total weight of the refrigerator system of the order of10 kilograms. As for the Stirling hot-gas engines, the Stirling-cyclerefrigerators of today are mechanically relatively complex, primarilydue to their use of two pistons with phase difference therebetween. Thismakes for an expensive design, mitigating against widespread use of thistype of refrigerator.

Among other refrigerators using gas-expansion principles with areciprocating piston can be mentioned the Gifford-McMahon-cyclerefrigerators. These devices are related to the Solvay refrigerationcycle, and employ a displacer piston with pneumatically controlledmotion, and a separate high-pressure source of working gas, e.g. from acompressor. Irreversible expansion are characteristic for theserefrigerators, and the associated entropy production lowers thethermodynamic efficiency to values considerably below the ideal Carnotefficiency. Therefore, the Gifford-McMahoncycle refrigerators are mostlybeing used in systems where thermodynamic efficiency and low powerconsumption are not of primary concern, but rather where reliability andmaintenance-free operation are essential, e.g. for airborne and militaryapplications. Refrigerators of this kind are described in the followingU.S. Patents: No. 2,966,035 to Gifford; No. 2,906,101 to McMahon;No.3,119,237 to Gifford; No. 3,188,819 to Hogan.

Other interesting gas-expansion refrigerators are the pulse tuberefrigerator by Gifford, No. 3,237,421, and the heat-poweredrefrigerator of the Vuilleumier type, which has received attention, egfor space and airborne cryogenic applications for small refrigerationloads. A recent embodiment of the Vuillemier refrigerator is describedin US. Pat. No. 3,423,948 to Cowan. A great number of gas-expansionrefrigerators with counter-current heat exchangers exist as well(reverse Brayton cycle, Claude cycle, etc.). These devices are not ofimmediate interest with reference to the present invention, since theydo not contain a thermal regenerator of the kind normally used in thisinvention. Only with reference to air dryers and heat pumps wouldcounter-flow heat exchangers be of great interest relative to thisinvention. Of no immediate interest are Joule-Thomson refrigerators orcommon two-phase refrigerator systems using freons and otherrefrigerants, since the present invention is primarily a single-phase(gas) device.

SUMMARY OF THE INVENTION The present invention provides an improved andsimple device for a hot gas engine or a gas-expansion refrigerator,using a new and simple method of performing the expansion step, and ifsuch is desired, recompressing the working gas with a simplereciprocating piston assembly. Basically, simple versions of theinvention employ two cylindrical work chambers of volumes which varyharmonically exactly or approximately 180 out of phase by virtue of asingle reciprocating piston assembly, or several pistons. Working gas isstored in a plenum chamber for closedcycle operation. The gas is allowedto flow from the plenum chamber, or from the ambient atmosphere foropen-cycle operation, into the so-called primary chamber, first passingthrough a valve arrangement of suitable kind, though a thermalregenerator, and finally through a heat exchanger (heat for the engine;refrigeration-load heat exchanger for the refrigerator). With cold-gasbleed for the open-cycle refrigerator the heat exchanger may beeliminated, and the heat load presented to the thermal regenerator bythe discrepancy in mass of inflow and outflow through the regenerator.The gas is permitted to flow into the primary chamber during acontrollable portion of the forward piston motion in which the volume ofthe primary chamber increases. In the reverse" stroke, gas from theprimary chamber is permitted to flow through the mentioned heatexchanger and thermal regenerator, and through the mentioned valvemechanism, or through another separate valve, into the secondarychamber, where the volume is now increasing. This transfer of gas fromthe primary to secondary chambers is performed in a nearly reversiblefashion, in contrast to e.g. Gifford-McMahon devices, by the veryimportant fact that the flow into the secondary chamber is initiatedwhen the volume of this chamber is zero (ideal case) or small, and henceno or little irreversible free expansions will take place. In thesubsequent forward stroke the work gas trapped in the secondary chamberis recompressed to the pressure level of gas in the plenum chamber(closed-cycle operation), or to a suitable level (open-cycle operation)for exhaust. The suitably recompressed work gas is permitted to leavethe secondary chamber through still another valve mechanism, which maybe integrated with one or both of the first mentioned valves, and flowsinto the plenum chamber, or into the ambient atmosphere for opencycleoperation. For closed-cycle operation, working gas is cooled preferablyin the plenum chamber to the original temperature, and can thereafter beused to perform a new work cycle.

The mentioned valve mechanisms could be of various types, e.g., diskvalves, sliding linear valves, or rotary valves. Proper synchronizationbetween the valve action and the piston position (or shaft angle) couldbe achieved in many ways, e.g., with help of cams followers on therotating shaft, or simply by placing a rotating valve or severalrotating valves on the main rotating power shaft, or on a shaft thatrotates with the same angular speed as the main shaft for thereciprocating piston motion.

In the transfer flow from the primary to the secondary chambers, the gaspressure should be lower than during injection into the primary chamberin order to obtain the correct thermodynamic overall cycle. This couldbe accomplished by a proper selection of crosssection area ratios of theprimary and secondary chambers, and/or'proper termination of the flowinto the primary chamber during the forward piston stroke. Withinjection during the full forward stroke for an engine, as a specialcase it is possible to employ an effective area ratio 1:1, which casecould be of significant practical interest. For the refrigerator, anarea ratio of 1:1 must always be accompanied by terminated injectionduring the forward stroke, at least for cases with no cold-gas bleedfrom the primary chamber. Secondary chambers with considerably smallereffective cross sectional area than that of the primary chamber can beused in the device of the invention is conjunction with injection onlyduring a small fraction of the forward stroke, but this would be ofpractical interest primarily only to the engine.

The thermodynamic processes involved with devices of the invention aredifficult to describe accurately, in particular since different portionsof the work gas undergo different thermodynamic paths, e.g. whendescribed in a temperature-entropy diagram. However, using a simplemodel for an average gas element it is easy to verify that thethermodynamic path is a loop of the desired kind for the closed cycle,with a calculable net amount of mechanical energy that can be extractedfor the engine, and a refrigeration-load for the refrigerator. Formoderate overall pressure ratios for the work cycle, e.g. ranging from 2to 5, the computed thermodynamic efficiencies according to ideal modelsare very high, indicating a performance of devices of the invention thatpotentially could be brought close to that of an equivalent Carnotcycle. Realistic calculations show efficiencies which in fact are betterthan for common Stirling-cycle devices, primarily due to superiorcooling characteristics and lack of cooler deadspace for devices of thisinvention. a

The mechanical output for the engine of the invention, and the coolingand load characteristics of the refrigerator can be controlled andregulated in a multitude of ways. The invention includes means forproviding this control. A simple principle of regulation and control isto connect the plenum chamber (or another special chamber) with any orboth of the work chambers during particular phases of the piston motion,and thereby controlling the pressure ratio of the cycle. The plenumchamber is then acting as deadspace during part of the cycle. Thementioned valve mechanisms can be used for this purpose, e.g. by usingthree-dimensional cams (with axial) movement) for a disc valve assembly.Alternative schemes could use a separate dead-space chamber or multitudeof chambers that fully or stepwise could be connected to the workchambers continuously during the work cycle. As a special example of thefirst mentioned control technique, we mention termination of the gasflow from the plenum chamber into the primary chamber at an appropriateearly position of the piston in its forward stroke. Hereby the amount ofwork gas entering the device each cycle can be controlled, and as aresult thereof also the power output for the engine, or heatloadcharacteristics of the refrigerator. Maximum power for the engine may beachieved if the injection is terminated, e.g. after the piston hasperformed threequarters of the forward stroke. Still another controltechnique is direct control of the pressure level in the plenum chamber.This could be done by help of hydraulic and pneumatic means, but couldbe power consuming and therefore is not a favored control technique.

The advantages of the invention will be readily understood from thedescription of the preferred embodiments thereof. However, we summarizeobvious advantages of the closed-cycle engine of the invention in thefollowing list.

1. Possibility of using only one piston or piston assembly, as comparedwith two pistons in common Stirling-cycle engines. This permits simplemechanical construction, low weight, and low production cost.

2. More efficient cooling system as compared to other hot gas engines.With cooling of the working gas taking place in a separate loop (in theplenum chamber), the residence time for a working gas element in thecooler can be made suitably large as can the heat-transfer area, and theheat-rejection fluxes conveniently low, in certain cases permitting theuse of a gaseous coolant (e.g. ambient air). The cooling could thereforebe more complete, and hence also the thermodynamic efficiency largerthan for conventional Stirling engines.

3. The decoupled cooler does not introduce any dead-space effect, a factwhich further increases the efficiency of such an engine.

4. No balancing buffer gas is needed, in contrast to recent Stirlingengines employing rhombic-drive mechanisms and high pressures for theworking gas. With this invention the power output means could beimplemented with a relatively thin piston rod, or simply with the crankmechanism located between the two work chambers.

5. With air as coolant, heated air from the cooler could be used in thecombustion process in the burner and heater. Reductions in weight andmanufacturing cost can be made with such a scheme, in part from the factthat a single device (e.g. impeller) can be used for propelling this airboth through the cooler and through the heater.

6. Possibility of locating the cooler and plenum chamber remote from thework chambers. This could be a most important feature for engines usedin automobiles. Possibility of using a filter in the plenum chamber.

7. Simple and efficient control and regulating possibilities.

8. Multiple-cylinder arrangements can use a common cooler and plenumchamber.

9. Multiple-cylinder arrangements can be built mechanically simple witha high power/weight ratio.

10. For certain applications air could be used as working gas. Sealingproblems would then be less severe, since gas lost by leakage couldsimply be replaced from the ambient atmosphere. In common Stirlingengines air is a less favored working gas, in part due to difficultiesin cooling the gas in the cooler (air has much smaller thermalconductivity than helium or hydrogen).

Advantages of the refrigerators of the invention (closed or open cycles)are summarized as follows 1 1. Highly efficient cooling system. Superiorcooling performance is of primary importance in obtaining lowtemperatures and refrigeration-load/power ratios.

12. Highly reversible flow. Refrigerators of the invention can be builtto give a minimum of irreversible entropy production, resulting in highoverall efficiency.

13. Multiple-step staging possible with simple means. Two or more stagescan be used for generation of very low temperatures, without addition ofvalves, and with a simple extension of the piston assembly to includeadditional work portions.

14. Open-cycle refrigerators can be built with extreme simplicity,without the use of heat exchangers other than the thermal regenerator.Such devices could be used for heat-pump applications and forair-conditioning systems. With modifications they could be used as airdryers, or devices for producing cryogenic liquids. The heat-pumpapplication would be most interesting, since the coefficient ofperformance and hence the economy would be much better thanexistingsystems using two-phase refrigerator systems with heat exchangers.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a schematic view of a firstembodiment of a hot gas engine according to the invention, with acombustion heat source;

FIG. 2 is an idealized temperature-entropy diagram for a closed-cyclehot gas engine as shown in FIG. 1;

FIG. 3 is a diagrammatic view of another embodiment of the inventionwhich is a two-step recompression hot gas engine;

FIG. 4 is a schematic view of a further embodiment of the inventionwhich is a hot gas engine with its crank mechanism nearly perfectlybalanced and located between the work chambers;

FIG. 5 is a schematic view of still another embodiment of the inventionwhich is a double-acting hot gas engine with an oscillating shaft andvanes;

FIG. 5a is a schematic view of the output drive of the engine of FIG. 5;

FIG. 6 is a schematic view of another embodiment of the invention whichis a four-cylinder hot gas engine;

FIGS. 7a -7d are diagrammatic views illustrating some ways of regulatingthe power output of the hot gas engine of the invention;

FIG. 8 is an idealized temperature-entropy diagram for a closed-cyclerefrigerator of the invention;

FIG. 9 is a schematic view of still another embodiment of the inventionwhich is an open-cycle refrigerator with cold-gas bleedoff;

FIG. 10 is a schematic view of a further embodiment of the inventionwhich is a simple open-cycle refrigerator with cold-gas bleedoff;

FIG. 11 is a schematic view of another embodiment of the invention whichis a refrigerator with phase difference between the two pistonsoperating in the primary and secondary chambers, respectively, andparticularly adapted for refrigerators with large cold-gas bleedoff;

FIG. 12 is a schematic view of a further embodiment of the inventionwhich is an open-cycle refrigerator with a primary counter-flow heatexchanger and two-step expansion, without recompression of the workinggas;

FIG. 13 is a schematic view of another embodiment of the invention whichis a two-step cooling device;

FIG. 14 is a schematic view of still another embodiment of the inventionwhich is a three-step cooling device;

FIG. 15a is a schematic view of a further embodiment of the inventionwhich is an air dryer based upon the open-cycle refrigerator principle,and employing centrifugal separation of the condensed liquid in thethermal regenerator; and

FIGS. 15b-l5e are schematic views of alternate (stationary) regeneratorembodiments using counterflow heat-exchangers and valve additions, ofparticular use for air dryers and heat pumps, but also in particularcases for any of the other closed or open-cycle refrigerators or enginesof the invention.

DESCRIPTION OF THE PREFERRED EMBODIMENTS (ENGINE) Referring now to thedrawings, FIG. 1 discloses a hot gas engine generally indicated bynumeral 10. The primary cylinder chamber is denoted 12 and the secondarychamber 14. The piston 16 has two cylindrical portions of generallydifferent diameters, one cylindrical portion 16a moving in the primarychamber 12 formed by cylinder 18, and the other portion 16b moving inthe secondary chamber 14 formed by cylinder 20. The piston is connectedto rotatable shaft 22 for extraction of mechanical energy by means ofconnecting rod 24, and crank 26. The portion of cylinder between pistonportions 16a and 16b is maintained at an arbitrary pressure level, e.g.,the ambient pressure by means of port 20a formed in the cylinder wall.The shaft could be connected to a flywheel arrangement, if desired, thatcould store mechanical energy and maintain correct reciprocating pistonmotion even when energy from the gas is not added to the pistonassembly.

A thermal regenerator 28 is connected in series with a heat exchanger 30for addition of heat to the working gas. The regenerator could be ametal matrix, sintered material, a bed of pebbles, packed metalwire-mesh, etc., or a counterflow heat-exchanger with one-way channels(with additional valving to achieve one-way flow in each leg). Theregenerator is used for temporary storage of heat of the oscillatingworking gas. For the engine the regenerator matrix receives thermalenergy from the working gas leaving the primary chamber, and

adds the same amount (ideally) to gas flowing into the primary chamber;for the refrigerator to be described later, the regenerator receivesthermal energy from gas entering the primary chamber, and returns thesame amount of energy when the working gas leaves the same chamber.Hence, ideally the regenerator is in no thermal contact with any othermaterial than the working gas.

Ambient air is fed into the heater assembly 31 (which includes burner36, e.g. for a liquid petroleum fuel, and heat exchangers 30 and 34),from line 32, through heat exchanger 34, preferably of the counterflowtype, and into the burner 36. The fuel is fed into the burner throughline 38. The products of combustion in burner 36 are fed through line 40into the,

heat exchanger 30, where heat is transferred to the working gas, whichcould be helium, hydrogen, or air, etc. FIG. 1 is only schematic, and inpractice the burner and heat exchanger 30 could be integrated into asingle unit. From the heat exchanger the combustion products are fedthrough line 42 back into the counterflow heat exchanger 34, wherefurther heat is transferred to the incoming air, and finally exhaustedthrough line 44. The counterflow heat-exchanger 34 could be replaced bya suitable thermal regenerator, e.g. by a rotating regenerator of metalor ceramic material.

The hot gas engine shown in FIG. 1 has a combined cooler and plenumchamber 46, in which working gas is cooled with help of a coolantcircuit, and working gas can be stored at a convenient working pressurefor the engine. The coolant (liquid or gaseous) flows into the coolerthrough line 48 and out of the cooler through line 50. The working gasenters the cooler 46 through line 52, and leaves the cooler through line54. The volume of the Plenum-cooler 46 is preferably larger incomparison to the swept volume of the piston in the primary chamber. Theadvantage of a large plenumcooler is that it affords a large residencetime for the gas in the plenum-cooler; this residence time could be mademany times larger than the period of one work cycle. The heat fluxesthrough the cooler could then be made relatively small, and theefficiency of the cooler high, and in certain cases direct gaseouscooling (e.g., ambient air) could be used. With ambient air as thecoolant, the coolant flowing from the cooler in line 50 may be feddirectly into line 32 of the heater, with or without a certain amount ofbleedoff, and used in the combustion process. The flow of coolant aircan be sustained with the help of an impeller arrangement (not shown),that could be coupled to the rotating shaft 22 (or preferably geared toa higher rotational speed than provided by shaft 22). Pumping aircoolant could alternatively be achieved by using the harmonicallychanging volume between pistons 16a and 16b in cylinder 20, and an addedcheck valve.

The hot gas engine is shown with a general 3-port 2- way valve 56, and a2-port l'way valve 58, for control of the flow of work gas through theengine. These valves could be combined into a single valve assembly, orfurther divided into e. g., a total of three 2-port l-w ay valves of asuitable type (disc valves, sliding valves, rotating valves, etc.). Thevalve action could be controlled in many different ways, but generallymost simply by coupling to the rotating shaft 22. This coupling isindicated schematically in FIG. 1. The coupling could be eliminated ifvalve 58 is a simple check valve, or could include cams and camfollowers if valve 56 is two disc valves, etc. The arrangement shown inFIG. 1 will suffice for thedescription of the operating principle ofthis type of engine which now.

follows.

Let us assume that quasi-steady conditions have been established,particularly with regard to the temperature profile in the regenerator.The right hand side of the regenerator 28 then has a temperature closeto the temperature of gas in the plenum-cooler 46, and the left handside of the regenerator has a temperature close to that of the heatexchanger 30, with a continuously changing temperature profiletherebetween. Thermal conduction inside the regenerator (from left toright) should preferably be small compared to the heat flux through theheat exchanger 30. The work cycle can be described thermodynamicallywith the aid of FIG. 2 which is a strongly idealized and schematictemperatore-entropy diagram for an average gas element flowing throughthe closed-cycle engine. The volume of the plenum-cooler is assumed tobe much larger than the swept volume of the piston, so that the flow ofgas from the plenum-cooler 46 into the primary chamber 12 takes place atapproximately constant pressure, as indicated by the straight line 60(isobaric line) in the diagram which employs a logarithmic temperaturescale and a linear entropy scale. The plenum-cooler exit condition isdenoted 62.

The flow into chamber 12 is preferably initiated when the volume of thatchamber is near its minimum, and is achieved by actuating valve 56 (FIG.1), to connect the plenum-cooler to chamber 12 through regenerator 28and heat exchanger 30. When the work ing gas flows from the plenumchamber through the regenerator, the gas temperature is raised bytransfer of heat (with a small temperature difference between the gasand the regenerator working elements) from the regenerator. Working gasleaves the thermal regenerator 28 with a temperature and thermodynamiccondition indicated by point 64 in FIG. 2. The flow of gas into theprimary chamber 12 can be terminated well before the shaft 22 hasrotated to a position at which the primary chamber has maximum volume.Depending upon the geometry and desired characteristics of the engine,the termination can take place, e.g., between 25 percent and 100 percentof the forward stroke, with an optimum termination point e.g. nearthree-quarters of the forward stroke. Valve 56 is then actuated to breakthe path from the plenum chamber to the primary chamber 12.

The path between the primary and secondary chamhers is preferablyconnected by means of valve 56 when the secondary chamber 14 has minimumvolume, in order to avoid possible free expansions and flowirreversibilities. In the following reverse piston motion, the gas inchamber 12 is forced to flow back through the heat exchanger 30 andthermal regenerator 28, into the secondary chamber 14. During thistransfer flow process the gas pressure is lower than the injectionpressure represented by line 60. Depending upon the area ratio of theprimary and secondary chambers and the temperature ratio across thethermal regenerator the pressure during the transfer process maydecrease,

l0 stay constant or even increase. FIG. 2 relates to a preferred casewith decreasing pressure. The isentropic expansion along line 66 topoint 68 for the average gas element is then caused by the transferprocess, with the element still located in the primary chamber, butcould in part also be caused by an expansion following a terminatedinjection in the forward stroke.

When the average gas element enters the heater during the reverse strokean isobaric heating process takes place, provided that the dead-space ofthe heater can be considered small and negligible (strong idealization). The gas element leaves the heater at point 72 in thetemperature-entropy diagram. In the regenerator, the gas transfers heatto the regenerator, as indicated by the isobaric line 74, the coolingprocess ending in point 76 at the exit of the regenerator.

In the present case with decreasing pressure during the transfer flow,the gas flowing into the secondary chamber mixes with slightly coldergas. This mixing process is generally accompanied by an overall increasein entropy, which is generally small and could be ignored in afirst-order analysis. In FIG. 2 we neglect such a mixing process andshow an isentropic line 78 for the further expansion of the average gaselement in the chamber 14. The minimum pressure of the cycle is reachedat point 80, when the volume of the secondary chamber is maximum. Itshould be noted that if the area ratio of the work chambers were chosensuch that the gas pressure was increasing during the transfer flow (thisprocess is not shown in FIG. 2), the minimum pressure of the cycle wouldhave to occur at the end of the forward stroke for gas located in theprimary chamber, having experienced an expansion following theterminated injection process.

In the following forward piston motion, the average gas element in thesecondary chamber is compressed as indicated along line 82 to point 84,at which point the pressure is the same as in the plenum-cooler 46.Valve 58 is then opened (guided valve or check valve) from its closedposition, in order to let gas flow through line 52 into theplenum-cooler 46 during the final portion of that piston stroke.

As shown in FIG. 2, working gas that enters the plenum-cooler has ahigher temperature (point 84) than when leaving the plenum-cooler (point62). The average gas element is cooled along the isobaric line 86 to theoriginal condition 62, and the thermodynamic path is closed. A necessarycondition for the averagegas model is that the regenerator hastransferred zero net amount of heat to the gas, per cycle. Therefore, ina normal temperature-entropy diagram employing a linear temperaturescale, the area a line corresponding to line 60 to the entropy axis mustbe identical with the area under a line corresponding to line 74 to theentropy axis, according to fundamental thermodynamic theories. In such adiagram (linear temperature axis), the net heat addition per unit mass.of the average gas in the heat exchanger 30 would be represented by thearea under the corresponding line 70, and is generally smaller than theheat which is temporarily transferred to the gas from the regenerator,represented by the area under a line 60 in the modifiedtemperatureentropy diagram. From this we can see that the regenerator isa significant element in the engine of the invention.

The thermodynamic process described in FIG. 2 is only approximate butcan nevertheless be used for evaluating performance characteristics ofthe hot gas engine. Calculations with such a model, and also with muchmore accurate models, show that the anticipated thermodynamicperformance of the device could in deed be high, and generally close tothe Carnot-cycle performance. This is particularly true when the overallpressure ratio of the work cycle is kept moderate or small. For apractical engine the net power output per cycle is of importance, aswell as efficiency. Therefore the overall pressure ratio cannot be keptclose to unity as efficiency considerations would dictate, but ratherbetween two and eight for a practical design.

It should be obvious with the simplified model of FIG. 2 that thethermodynamic processes involved in the hot gas engine of the inventionare practically reversible in all separate steps. Entropy-producing freeexpansions are avoided, as well as throttled flows, since these havestrong adverse effect upon the efficiency. With finite volumes of theregenerator, heater, and the channels from the primary to secondarychambers, and hence non-negligible dead-space, the valve actions couldbe modified to completely avoid free expansions. For example, valve 56could be actuated to close the path between the regenerator 28 and thesecondary chamber 14 before the piston has reached the left turningpoint in the reverse stroke; the closing could be such that gas in theregenerator, heater and primary chamber is recompressed to theplenum-cooler level in the very last portion of the reverse stroke,after which valve 56 is actuated to open the path between theplenum-cooler and the primary chamber.

FIG. 3 shows a hot gas engine employing recompression in two steps withthe help of a third work chamber 88, formed by the piston and thecylinder 20. Besides the first plenum-cooler 46, a second plenum-cooler90 could be used, operating at a higher pressure level. Additionalvalves are used, here shown as check valves 92 and 94. These could bevalves of any suitable type and controlled not by the gas pressure asindicated, but by the shaft angle as for valve 56 (e.g. cam, camfollower and disc valve). In the embodiment of FIG. 3, gas in thesecondary chamber 14 is forced into the plenum-cooler 46 through thevalve 58 at minimum pressure loss, when the pressure in the secondarychamber is raised to a desired level (equal to the gas pressure in theplenum-cooler 46) in the forward stroke. During the same stroke, anotherportion of g as flows from the plenum-cooler 46 through valve 92 intothe compression chamber 88. Final compression takes place in the reversestroke in chamber 88, to the pressure level of the plenum-cooler 90. Inthe final part of that stroke, the valve 94 is opened and gastransferred from chamber 88 into the plenum-cooler 90, where the gas iscooled to its original temperature. The steady-state pressure level ofthe first plenum-cooler 46 will depend upon the relative sizes ofchambers 14 and 88, as well as the cooling in plenum-cooler 46. Amongadvantages of two-step or multiple-step recompressions can be mentionedthe possible reduction in the total amount of heat that has to berejected in the coolers, for a given overall pressure ratio of thecycle, as well as a possible increase in the net power output andthermal efficiency due to less compression work necessary. Another advantage could be better balancing and distribution of angular moment onthe output shaft 22. In practice, these features should have to beweighed against the added mechanical complexity with two-steprecompression.

FIG. 4 shows another embodiment of my hot gas engine. The rotatingoutput shaft 22 is here placed between the primary chamber 12 and thesecondary chamber 14. For simplicity, we have chosen the same diameterfor these chambers and piston portions 16a and 16b, making the designattractively simple. A bevelled gear 96 on the shaft 22 drives a pinion98 and another bevelled gear 100, which is coaxial with the gear 96, andcounter-rotating. Two connecting rods 24 are used to rotate the pistonassembly 16. The rods are each fastened to a respective one of thecounter-rotating gear wheels. Counter-weights 102 and 104 are shownschematically attached to each of the gears. With this arrangement apractically perfect balanced engine can be obtained, and with nosignificant side forces on the piston assembly. Such an absence of sideforces is desirable in solving the sealing problem, and would permit anevenly distributed wear on piston rings, etc.

The valves 56 and 58 are here shown as rotating valves, located directlyon the axis of gear 100. The valve action is the same as described forthe engine in FIG. 1. The output power is delivered during the firsthalf of the forward stroke with this type of engine. Therefore, theengine could preferably be equipped with a flywheel arrangement forsmooth constant angular speed of shaft 22. The flywheel could preferablybe located on one of the gear shafts, or to another highspeed shaft,geared to any of the original shafts. The plenum-cooler 46 is shownschematically and not in proper size relationship to the primary andsecondary chambers. The plenum-cooler is preferably large with respectto the chambers as for prior embodiments; the principles discussed forFIG. 1 as to the size of the cooler also holding here.

FIG. 5 and FIG. 5a show a hot gas engine having an oscillating mainshaft in a double-acting mode. The rotation of shaft 22 is developedfrom the oscillating motion of shaft 106 by means of crank 26 and rod24. Several other schemes of generating the oscillating motion andlimitation of the rotation angle are possible, but they shall not befurther discussed here since such configurations are widely known. Twovanes 108 and 110 are fastened to the oscillating shaft 106 andconstitute moving walls in the chambers 112, 114, 116 and 118. Chambers112 and 114 constitute one basic hot gas engine, and chambers 116 and118 another, with a common plenum-cooler 46. The A-engine (112 and 114chambers) and the B-engine (116 and 118 chambers) have individualheaters 30a and 30b and regenerators 28a and 28b. If desired, theheaters could be partially integrated. The vane 108, oscillating in theprimary chambers 112 and 116, is shorter than the vane 110. Therefore,the maximum volumes of the primary chambers are smaller than those forthe secondary chambers, as for the engine of the embodiment of FIG. 1.The total angular motion of the oscillating shaft 106 is limited to lessthan The four valves 56a, 56b, 58a and 58b could be of any suitable typeand, for example, integrated and located on a rotating shaft in phasewith shaft 22, and operated in the same basic manner as described forthe embodiment of FIG. 1. This double-acting hot gas engine could bedesigned to deliver a positive amount of mechanical power to therotating shaft 22 for typically half the period of a 360 rotation of theshaft. A flywheel could preferably be connected to the output shaft, orto a shaft geared to shaft 22.

FIG. 6 shows a hot gas engine of the invention with a multiple cylinderarrangement. Four separate work cylinders 20a-20d are shown, each ofconstant crosssectional area, similar to the engine of FIG. 4. Eachcylinder has an individual regenerator 28a-28d, but the heater 30 ispartially common for the work cylinders, and the plenum-cooler iscompletely common for all cylinders. As indicated in the figure, theplenum-cooler could be remotely located without dead-space penalty, anadvantage, e.g., for automobile-engine applications. The valves 56 and58 (of the embodiment of FIG. 1) are in the embodiment of FIG. 6integrated into valves l24a-124d of the 4-port 3 way type. The valveunits 124a-l24d could again be e.g., cam-guided disc valves or linearvalves, or valve of rotating types mounted on a shaft rotating in phasewith the main shaft 22. Bevelled gears 96 and pinions 98 are utilized asin the embodiment of FIG. 4, in order to achieve good balancing andsmall side forces on the pistons. Naturally, other known crankmechanisms can be used as well. A single flywheel is attached to themain shaft 22 (two counterrotating flywheels could preferably be used ontwo counter-rotating gear wheels in order to eliminate possible stronggyroscopic effects). The work pistons in FIG. 6 are arranged with 90phase difference, in an individual order that could be changed.

FIGS. 7a-7d show schematically three ways of regulating the power outputfrom a hot gas engine by changing the valve opening and closingcharacteristics. FIG. 7a shows a basic hot gas engine of the inventionwith a schematic 4-port 3-way valve 124, replacing the two valves 56 and58 in FIG. 1. The possible paths of gas through this valve are denoted Ifor injection into the primary chamber, II for the transfer flow to thesecondary chamber, and III for the exit flow from the secondary chamber14 into the plenum-cooler. The crank angle of the main shaft is denoted41, with d for the piston at the left turning point. FIG. 7b showsschematically a preferred way of regulating the power output from theengine, namely by regulating the amount of injection of gas into theprimary chamber through control of path 1. Maximum power is hereobtained with curve 128, for shutoff of path I for a certain crank angleless than 180. Delaying shutoff as indicated by curve 130, the overallpressure ratio of the cycle is decreased and the mechanical power outputper cycle is decreased. The delay may continue to crank angles largerthan 180 if desired.

This regulating technique can be said to introduce the plenum-cooler asdead-space when the injection is not terminated according to the idealcurve 128 in FIG. 7b. The dead-space is only coupled to the work chamber12 for a fraction of the cycle. The control function can be controlledmechanically, e.g. with an axially moveable three-dimensional cam forthe case when cam, cam followers and disc valves are used, or byrotating the outer valve housing for a rotating valve,

or in any other known way generate the desired change in phase (withrespect to the crank shaft) of the closing of path I.

FIG. 7b shows the alternative regulating procedure, whereby path I isclosed earlier than normal, represented by line 132. This methoddecreases the mass flow through the engine compared to the first scheme,and also increases the overall pressure ratio of the work cycle (andtherefore slightly decreases the efficiency compared to the optimumvalue).

FIG. shows a second basic way of regulating the power output, which willgenerally be less preferred. The normal opening of path III (indicatedby curve 134) takes place at a crank angle for which the recompressionin the secondary chamber has proceeded to a stage at which the gaspressure equals the plenum-pressure. By delaying the opening of pathIII, e.g., as indicated by curve 136, additional pressure build-up inthe secondary chamber will take place, before the pressurized gas willflow irreversibly into the plenum-cooler 46. The result of such a delayis a lowering in the net mechanical power output per work cycle, butalso a lowering in the thermodynamic efficiency due to the flowirreversibility.

The technique of delaying opening of path Ill can be used even when thepath is regulated with help of a check valve. A special type of checkvalve could be employed using a variable counterpressure to a hydraulicor pneumatic circuit for the control. Such a regulating technique couldbe made relatively simple, and is to be preferred before a directmechanical control technique.

The normal closing of path III] takes place for as shown by curve 138 inFIG. 70. If this closing instead is delayed, as represented by curve140, and path II is opened in a normal fashion, the lowering of the gaspressure in the work chambers is prevented during the reverse stroke,and gas from the plenum-cooler redrawn into the work chambers throughline 52. This regulating scheme is essentially identical with thatdescribed in FIG. 7b by curve 1130, and could be a favored scheme forcertain applications.

Finally, FIG. 7d shows power regulation by changing the opening of pathII from the ideal, as represented by the curve 142, to a delayedopening, as represented by curve 144. This scheme gives entropyproduction from irreversible flow into the secondary chamber, but couldbe effective in rapidly stopping or slowing the engine.

Other power regulating techniques than the mentioned ones could be used.A simple method could make use of a separate dead-space chamber ofvariable volume, which could be connected to any of the work chamberscontinuously during the work cycle (previous methods used interruptedconnection with the plenum-chamber dead-space). With the dead-spacebeing minimum the power output would be maximum. The dead-space could becontinuously variable, e.g. with help of a hydraulically actuated pistonin a cylinder deadspace. Alternatively, step-wise changing of thedead-space volume could be used with help of a series of smallerdead-space chambers that could be connected one by one with the workchambers, by help of a valve arrangement (e.g., sliding valve). Stillother power control schemes are possible whereby the pressure level ofthe plenum-cooler (and possible the introducing plenum-cooler volume)are directly changed. Many variations are possible here, e.g. usingseparate gasstorage chambers of different pressure than the main plenumchamber, using hydraulically actuated pistons to compress gas in theplenum-cooler, and special devices for limiting the amount of gas in theplenumcooler that can flow into the primary chamber (without unnecessaryirreversibilities). These schemes shall not be further discussed here,since they are known within the art.

While the engine of the invention has been described by reference topreferred embodiments, it should be apparent that numerous changes couldbe made within the spirit and scope of the invention disclosed herein.Some of the possible features are discussed in the following sections ofpreferred embodiments for the refrigerator, and many of the discussedengine features can be used for the refrigerator of the invention.

DESCRIPTION OF THE PREFERRED EMBODIMENTS (REFRIGERATOR) For therefrigerator we shall discuss both closedcycle and open-cycle devices.The closed-cycle refrigerators have much in common with the previouslydescribed closed-cycle hot gas engines. Open-cycle engines have not beendiscussed in detail or in the drawings of preferred embodiments, mainlydue to the relatively low power output per unit swept volume, whenoperated with ambient air as the working medium.

We first discuss the closed-cycle refrigerator in thermodynamic detailusing the average gas model, as for the engine. FIG. 8 shows the closedthermodynamic path with the average gas model (strongly idealized).Basically, the refrigerator is operated similarly to the engine, butwith the difference that the heat exchanger 30 is now a simplerefrigeration-load heat exchanger 30, with a temperature lower than thegas in the plenum-cooler 46, and that mechanical energy has to bedelivered to the shaft 22 in FIG. 1, instead of being extractedtherefrom. FIG. 8 relates to a refrigerator with decreasing pressureduring the transfer flow process, i.e. to a case when the effectivecross section area of the secondary chamber is at least as large as thatof the primary chamber. As mentioned earlier, the refrigerator of theinvention could be operated in a mode with increasing (or constant)pressure during the transfer flow, provided that an initial expansion inthe primary chamber takes place during the later portion of the forwardstroke. Such a refrigerator could utilize a secondary chamber with evenequal of smaller crosssection area than that of the primary chamber, butwill not considered in FIG. 8.

Referring to FIG. 8, the average gas element leaves the plenum-cooler 46(in a configuration as FIG. 1) with the thermodynamic conditionindicated by point 146. Thereafter, the gas flows through the thermalregenerator (ordinary thermal regenerator or counterflow heat-exchangerwith two one-way legs) along path 148 of constant pressure to point 150,which ideally has the temperature of the refrigeration-load heatexchanger 30. In the primary chamber 12 the gas element is expandedadiabatically in the reverse stroke, as indicated by line 152, to point154. The average gas element then returns through the refrigeration-loadheat exchanger 30, receiving the refrigeration load as shown by path156, to point 158 (having the same temperature as point Therefrigeration load accepted by the gas element per unit mass isrepresented by the area under line 156 in a temperature-entropy diagramwith linear temperature scale (FIG. 8 employs a logarithmic scale). Thegas element returns further through the regenerator 28 and is thenreheated by the regenerator matrix to point 160, which has thetemperature of gas leaving the plenum-cooler, in this idealizedtreatment.

Before completion of the reverse stroke, the average gas elementundergoes additional expansion, along an isentropic line 162 to point164, which has the lowest pressure of this ideal cycle. Therecompression takes place ideally along path 166 to point 168 (withpressure identical to point 146). Finally, the gas element is cooled inthe plenum-cooler along the isobaric line to point 146, and thethermodynamic path is closed.

For an open-cycle, the gas element under study is simply exhausted atpoint 168, provided that employed inlet and exhaust pressures are equal,and the refrigerator not driven fully or partially with pressurized gas.Such a device will be discussed later.

With the idealized refrigerator model of FIG. 8, the refrigeration-loadwas applied in a separate heat exchanger 30. Naturally, in a practicalsituation no such separate exchanger may be required, and the loadapplied e.g. directly to the walls of the primary chamber, or to otherheat-exchanging surfaces that the working gas can be in contact with.The same argument could hold for the heat rejection in theplenum-cooler. Part or all of the heat rejection could take placethrough a heat exchanger (not shown in any of the figures) located inthe secondary chamber or in the gas line to the right of the thermalregenerator, or simply by cooling the walls of the secondary chamber.However, for already discussed reasons, the major portion of the coolercould preferably be located in the plenum chamber for closed-cycleoperation.

FIG. 9 shows an open-cycle refrigerator with cold gas bleedoff, withouta refrigeration-load heat exchanger. This refrigerator is speciallyadapted for cooling an enclosed volume of gas (air), and transfers theabsorbed heat from this volume to gas located outside the enclosedvolume (the ambient air). The enclosed volume is assumed to contain gaswhich is substantially cooler than the ambient gas. For optimumefficiency, the refrigerator is equipped with two thermal regenerators28 and 170, one cold gas inlet 172 from the enclosed volume, one warmgas inlet 174 from the ambient atmosphere, a still colder gas outlet 176(into the enclosed volume), and a still warmer gas outlet 178 (to theambient atmosphere). The necessary valves are here shown as five 2-portl-way valves 180, 182, 184, 196 and 190. These valves could be combinedinto fewer units, as discussed previously for the engines.

The open-cycle refrigerator in FIG. 9 can be operated in several ways,e.g. as follows: At the first portion of the forward stroke, valve 182is kept open to permit cold gas to flow through the regenerator 28 intothe primary chamber 12. The right side of the regenerator 28 has atemperature which ideally is close to the inlet temperature in channel172. Thereafter, in a later portion of the forward stroke warm gas fromline 174 is fed through valve 184 and through both re-generators intothe primary chamber. The right side of the regenerator 170 has atemperature at steady-state condition which ideally is close to thetemperature of gas in the warm inlet line 174. The injection of gasthrough line 174 could be terminated at an arbitrary point of theforward stroke, e.g. at the end of the stroke, and for which case theeffective area of the secondary chamber must be larger than that of theprimary chamber (as shown in FIG. 9). With the primary and secondarychambers made up from a single constant-diameter tube, the injectionthrough line 174 must be terminated before the end piston has completedthe forward stroke. In the reverse stroke still colder gas is forcedthrough valve 180 to the exit line 176, followed by the transfer processof the remainder of the gas in chamber 12 to chamber 14 through valve190. In an alternative scheme the transfer process could take placebefore ejection of gas through line 176, in the reverse stroke, wherebyentropy increase would be less and the overall thermodynamic efficiencyideally better.

The cold gas that is bled through valve 180 has attained the lowertemperature from the falling temperature profile in regenerator 28(going from to left). The amount of bleed is controlled by valve 180 andshould be identical with the amount of gas taken in through line 172.

If the cold gas bleedoff takes place before the transfer flow in thereverse stroke, the valve 190 should not be opened until valve 180 isclosed. If no backfiow has been permitted through valve 186 into thesecondary chamber during the cold-gas bleedoff, a free expansion willtake place when valve 190 is opened that have an adverse effect on theoverall efficiency of this refrigerator. For this reason such backflowcould preferably be used.

In the forward stroke, valve 186 is opened when the gas pressure in thesecondary chamber has been raised to the ambient level, and the stillwarmer gas exhausted through line 178. Valve 186 could be a simple checkvalve if no backflow of the mentioned kind is desired.

With this type of refrigerator, bleeding an intermittent flow of coldgas without the use of refrigerationload heat exchangers, the load isobviously placed upon the regenerators. With the refrigerator of FIG. 9the load is on regenerator 28, and gas from the ambient atmosphere usedin the work cycle to maintain the desired falling temperature profile inregenerator 28 for cooling of the cold gas, and for transport of theheat (and mechanical power from the shaft converted to heat) to theambient atmosphere. The thermodynamic characteristics of such systemshave been computed using gas models as shown in FIG. 8, as well as withcorrect infinite element models. With cold-gas bleedoff a fundamentaldifficulty exists in the treatment of the energy balance of theregenerators, due to the fact that the regenerator experiences a netmass flow and a small amount of entropy has to be generated from heattransfer in the matrix.

In the device of FIG. 9, the cold-gas bleed could be replaced with arefrigeration-load heat exchanger, with elimination of valves 180 and182. Naturally, the same open-cycle refrigerator could be modified toemploy closed-cycle operation for gas that flows through the secondarychamber and establishes the desired temperature profiles in theregenerator matrixes. In this case a cooler and a plenum chamber have tobe added in the normal fashion. Cold-gas bleedoff is maintained aspreviously described, with the cold-gas bleedoff rate equal to the rateof inlet flow for steady-state operation.

FIG. 10 shows a simpler open-cycle refrigerator than FIG. 9, with onlyone regenerator 28, one inlet 174, and a cold gas outlet 176, and a hotgas outlet 178. The valves 184 and 190 of FIG. 9 have been replaced inFIG. 10 with a single 3-port 2-way valve 192, with an operating functionsimilar to that of valve 56 in FIG. 1.

According to one operating scheme, permitting an arbitraty area ratiofor the work chambers, injection through line 174 is terminated beforecompletion of the forward stroke. In the reverse stroke the transferprocess is accomplished through valve 192, after which recompression ofgas in chamber 12 follows, and subsequently cold-gas bleedoff occursthrough line 176 when the pressure level in the primary chamber has beenraised to the desired level. A device of this kind could be built withthe primary and secondary chambers made from a single cylinder and asimple piston, and could be used for simple heat-pump or refrigerationapplications.

With the device shown in FIG. 10 recompression takes place in thesecondary chamber, with subsequent exhaust through valve 186 (checkvalve or mechanically controlled valve). The refrigeration load isapplied on the thermal regenerator as for the previously discussedopen-cycle device.

An alternative operating scheme with a device as shown in FIG. 10 couldemploy cold-gas bleed before the transfer flow process. Such a deviceshould not use an initial expansion following injection during theforward stroke, and must therefore necessarily have a larger crosssection for the secondary chamber. to accomplish a decreasing pressureduring the transfer process.

In order to avoid splitup in transfer flow and coldgas bleedoff duringthe reverse stroke, e.g. with the configuration of FIG. 10, a separatecold-gas storage chamber can be employed. Such a chamber would be filledduring the forward stroke, and emptied during the full reverse stroke.Overflow from this additional chamber to the primary and secondarychambers during the reverse stroke (with decreasing pressure in the lastchambers) can be prevented with help of a checkvalve arrangement. Theadditional chamber could be formed by help of an extension of the pistonand an additional cylinder. Such devices will be briefly discussed withregard to FIG. 13, and are within the spirit and scope of the invention.

FIG. 11 shows an open-cycle refrigerator similar to that of FIG. 10, butwith the basic difference that the piston assembly is divided in twoparts, with a phase difference in motion. This is accomplished with thetwo cranks 26 that have individual connecting rods 24. The part of thepiston assembly that reciprocates in the primary chamber 12 is in anearlier phase than the piston in the secondary chamber 14. With thisdevice, coldgas bleedoff through valve 180 can take place during thefirst portion of the reverse stroke of piston 16a (in the primarychamber), and the transfer flow can be initiated when the volume ofchamber 14 is minimum, i.e.

the flow into chamber 14 can be made in a reversible fashion. Properinitiation of the transfer flow is assured by valve 192, which in aconventional way could be guided by the angular position of the rotatingshaft 22.

The types of refrigerators shown in FIG. and FIG. 11 could be driven bypressurized working gas, or by a combination of pressurized gas andmechanical power into the rotatable shaft 22. With no mechanical energysupplied to the rotatable shaft 22, the working gas is then expandedwhen flowing through the refrigerator (the recompression could beeliminated), and the exit pressure is smaller than the inlet pressure.The crank mechanism of the rotating shaft is then used to control thelength of the piston stroke, to guide the valves (proper opening andclosing characteristics), and possibly also to provide a connection witha flywheel device for smooth reciprocating motion of the pistonassembly.

FIG. 12 is an example of an open-cycle refrigerator, driven bypressurized working gas, with the refrigeration load applied to a heatexchanger, and employing a two-step expansion process. The inletpressure in line l94 is higher than the exit pressure inline 196, herefed to the ambient atmosphere. No mechanical energy is supplied to shaft22, and mechanical energy may instead even be extracted through theshaft, or dissipated in an arbitrary fashion. An optional counterflowheatexchanger 198 is used for an initial cooling process, in which theincoming gas (line 194) transfers heat to the outgoing gas (line 196).The refrigeration load is applied to exchanger 30, thus implementing therefrigera tion. A third working chamber 200 is employed for the secondexpansion step in the transfer from the secondary chamber 14 to thischamber. Therefore, the effective cross-sectional area of the face ofthe piston 16b in chamber 200 is larger than in the secondary chamber14. An additional valve 202 (e.g. controlled by the angular position ofshaft 22) is used for the control of the second transfer flow intochamber 200. The geometry of the refrigerator is preferably adjustedsuch that the gas pressure in chamber 200 is identical with the ambientpressure (the pressure in the exhaust line 196) after the final transferflow to chamber 200.

Similar to the previous embodiments, the matrix of the regenerator has adecreasing temperature profile, going from right to left in FIG. 12.This temperature profile is established and maintained so that the gaspressure in the transfer flow process is lower than during gas injectioninto the primary chamber. Basically, the cooling in this refrigeratortakes place in two steps, first in the counterflow heat-exchanger 198,and thereafter in the regenerator 28. The decreasing temperature profilein the heat exchanger 198 (following the inlet gas) is maintained withhelp of the gas cooling from adiabatic expansion in the second transferflow from the secondary chamber 14 to chamber 200. The function of valve202 is to provide an open path between chambers 14 and 200 during theforward stroke of the piston. The function of valve 58 is to provide anopen path between chamber 200 and the exit channel 196 during thereverse stroke.

The average residence time of gas in the refrigerator of FIG. 12corresponds to nearly two complete piston cycles: injection into theprimary chamber 12 in the first forward stroke, transfer to thesecondary chamber 14 in the first reverse stroke, transfer to theadditional expansion chamber 200 in the second forward stroke, andfinally exhaust from chamber 200 to line 96 in the second reversestroke.

The refrigerator of FIG. 12 could be modified in a large number of ways.One modification could be elimination of both the heat exchanger 30 andthe regenerator 28, but with addition of one valve. This valve wouldprovide cold-gas bleedoff from the primary chamber. The cooling in sucha refrigerator would only be in one step, due to the transfer flow fromthe secondary chamber 14 to the additional chamber 200, and the primarychamber 12 used for pumping cold gas. Briefly, the operation of therefrigerator would involve the following steps: filling of the primarychamber 12 during the first forward stroke, filling of the secondarychamber from line 194 with help of valve 56 (this valve now has adifferent function) during the first reverse stroke, and cold-gasbleedoff from chamber 12 through the mentioned valve addition during thesame stroke, transfer flow under decreasing pressure from the secondarychamber to chamber 200 during the secondary forward stroke (by help ofvalve 202), new filling of the primary chamber 12 during the samestroke, and finally exhaust from chamber 200 to line 196 and coldhasbleedoff during the second reverse stroke. Since this refrigerator wouldoperate with full gas pressure of the source in chamber 14 aftercompleted reverse stroke, the pressure ratio for the device should besmaller than for the first described device, or alternatively theinjection from the source (line 194) into chamber 14 terminated beforecompletion of the reverse stroke, in analogy with schemes discussed forthe engine of the invention.

FIG. 13 shows a closed-cycle refrigerator with twostep cooling and threework chambers. The plenumcooler is not shown, nor are the rotatableshaft and crank mechanisms, that could be used to provide the properreciprocating piston motion. Two regenerators 28 and 204 are used, andan additional chamber 206 formed by the reciprocating piston and acylinder 207 with a larger effective cross-sectional area than cylinder209 (forming the cold chamber 12).

Chambers 14 and 206 could be made with the same constant-diametercylinder and hence with the corresponding piston portions of the samediameter, making the mechanical construction considerably simpler. Theoperation of such a device necessitates that the injection into chamber12 be terminated before the completion of the forward stroke, and isalso characterized by an increase in pressure during the transfer flowto chamber 14.

In understanding the operation of this device, the regenerator could beconsidered to operate in conjunction with the larger primary chamber 206and provide the first-step cooling, with the refrigeration load beingsecond step (heat exchanger 30, etc.). Hence, the colder primary chamber12 could be considered to be the primary chamber in a refrigerator withchamber 206 as the secondary chamber.

To adapt this refrigerator for use as an open system with cold-gasbleedoff with expenditure of gas from the gas source in line 54, theheat exchanger 30 would be eliminated and a bleed valve introduced nearthe chamber 12. If the bleed from chamber 12 takes place

1. In a gas compressing and expanding device for use as an engine orrefrigerator, primary and secondary gas work chambers, piston assemblymeans having first and second piston portions mounted for reciprocatingmotIon in said primary and secondary chambers respectively, said pistonportions being connected to each other so that with motion thereof, theeffective volumes of said chambers are varied in substantially inverserelationship, a source of gas, means for feeding gas from said gassource to the primary chamber during a first period of timecorresponding to a predetermined percentage of the forward stroke ofsaid piston assembly means, means for providing a fluid communicationspath between said primary and secondary chambers to transfer gastherebetween during a second period of time including at least a portionof the time of a predetermined reverse stroke of said piston assemblymeans, the average pressure of the gas when transferred being lower thanwhen fed to the primary chamber, said means for feeding gas to theprimary chamber and said means for providing a fluid communications pathbetween the primary and secondary chambers including common channelmeans comprising a thermal regenerator having a connection for each endthereof, one of said regenerator connections being coupled to saidprimary chamber, and valve means interposed between the other of theregenerator connections and the source of gas and the other of theregenerator connections and the secondary chamber for connecting saidsource of gas to said regenerator during said first period of time andsaid regenerator to said secondary chamber during said second period oftime, means for causing heat exchange with said gas, and means forreleasing gas from the secondary chamber during at least a portion ofthe forward stroke.
 2. The device of claim 1 wherein the first period oftime corresponds to substantially 75 percent of the forward stroke. 3.The device of claim 1 wherein the first period of time corresponds to25- 100 percent of the forward stroke.
 4. The device of claim 1 whereinsaid second period of time commences when the forward stroke has beencompleted.
 5. The device of claim 1 wherein said means for releasing gasfrom said secondary chamber comprises valve means for venting the gas tothe ambient atmosphere.
 6. The device of claim 1 wherein said means forreleasing gas from said secondary chamber comprises a plenum chamber andmeans for feeding the gas to the plenum chamber, said source of gascomprising the gas in said plenum chamber.
 7. The device of claim 1which is a refrigerator wherein is included means for driving saidpiston assembly means to cause the expansion and compression of the gasin said chambers, said means for causing a transfer of heat to said gascomprising a refrigeration heat load.
 8. The device of claim 1 which isan engine, said means for causing heat exchange with said gas includinga heater device.
 9. The device of claim 8 wherein said source of gascomprises a gas filled plenum chamber and means for cooling the gas insaid chamber.
 10. The device of claim 1 wherein said source of gascomprises the ambient atmosphere.
 11. The device of claim 9 wherein saidgas is air.
 12. The device of claim 1 wherein said piston assembly meanscomprises a central portion interconnecting said first and second pistonportions, said piston portions moving reciprocally parallel to apredetermined axis.
 13. The device of claim 9 wherein the volume of saidplenum chamber is substantially larger than that of said primary andsecondary chambers.
 14. The device of claim 9 wherein said cooling meanscomprises ambient air.
 15. The device of claim 1 wherein said pistonassembly means comprises a rotatably supported central shaft portion,said first and second piston portions comprising vane members extendingradially from said central shaft portion, said work chambers beingformed by a cylindrical member enclosing said piston portions.
 16. Thedevice of claim 1 wherein said means for causing heat exchange with saidgas further includes a heat exchanger.
 17. The device of claim 7 whereinsaid primary gas work chamBer is divided into a plurality of separatesections of different cross-sectional areas, said first piston portionincluding a separate piston member for each of said chamber sections.18. The device of claim 7 and further including a third gas work chamberpositioned between said primary and secondary work chambers.
 19. Thedevice of claim 7 wherein said heat transferring means includes aregenerator and condenser means attached to the regenerator forseparating condensable liquid from the working gas.
 20. In a hot-gasengine, primary and secondary gas work chambers, piston assembly meanshaving first and second piston portions mounted for reciprocating motionin said primary and secondary chambers respectively, said pistonportions being connected to each other so that with motion thereof, theeffective volumes of said chambers are varied in substantially inverserelationship, a source of gas, external heat source means for applyingheat energy to said gas, means for feeding the gas to the primarychamber during a first period of time corresponding to a predeterminedpercentage of the forward stroke of said piston assembly means, meansfor providing a fluid communications path between said primary andsecondary chambers during a second period of time including at least aportion of the time of a predetermined reverse stroke of said pistonassembly means, thermal regenerator means forming a common channelinterposed between said source of gas and said primary chamber forapplying heat to said gas as it flows to said primary chamber andinterposed in said path between said primary and secondary chambers forwithdrawing heat from the gas as it flows from the primary to thesecondary chamber, valve means interposed between the regenerator andthe source of gas and the regenerator and the secondary chamber forconnecting said source of gas to said regenerator during said firstperiod of time and said regenerator to said secondary chamber duringsaid second period of time, means for releasing gas from the secondarychamber during at least a portion of the forward stroke, and outputdrive shaft means coupled to said piston assembly means.
 21. The deviceof claim 20 wherein the first period of time corresponds to 25- 100percent of the forward stroke.
 22. The device of claim 20 wherein thefirst period of time corresponds to substantially 75 percent of theforward stroke.
 23. The device of claim 20 wherein the second period oftime commences when the forward stroke has been completed.
 24. Thedevice of claim 20 wherein said piston assembly means comprises acentral portion interconnecting said first and second piston portions,said piston portions moving reciprocally parallel to a predeterminedaxis.
 25. The device of claim 20 wherein said means for feeding the gasto the primary chamber and said means for providing a communicationspath between the chambers includes valves operatively responsive to theshaft means.
 26. The device of claim 20 wherein said piston assemblymeans comprises a rotatably supported central shaft portion, said firstand second piston portions comprising vane members extending radiallyfrom said central shaft, said work chambers being formed by acylindrical member enclosing said piston portions and having a separatorportion dividing said cylindrical member into said primary and secondarychambers.
 27. The device of claim 20 wherein said means for applyingheat to said gas further includes a heat exchanger.
 28. The device ofclaim 27 wherein said source of gas includes a plenum chamber filledwith gas and cooler means for cooling the gas in said plenum chamber,said means for releasing gas from said secondary chamber comprisingmeans for interconnecting the secondary chamber and the plenum chamber.29. The device of claim 20 and further including a third gas workchamber positioned between said primary and secondary chambers.
 30. Thedevice of claim 20 wherein said piston assembly means comprises acentral portion interconnecting said piston portions for reciprocalmotion in said chambers, said output drive shaft means being coupled tosaid central portion.
 31. The device of claim 20 and further including aplurality of additional primary and secondary chambers and pistonassembly means operating similarly to said first mentioned chambers andpiston assembly means, the piston portions of said various pistonassembly means all being coupled to said output drive shaft means, saidpiston portions being phased relative to each other to provide rotatabledrive of said drive shaft means.
 32. In a refrigerator, primary andsecondary gas work chambers, piston assembly means having first andsecond piston portions mounted for reciprocating motion in said primaryand secondary chambers respectively, said piston portions beingconnected to each other so that with motion thereof, the effectivevolumes of said chambers are varied in substantially inverserelationship, means for driving said piston portions reciprocally insaid chambers, a source of gas, means for providing a refrigeration heatload, means for feeding said gas to said primary chamber during a firstperiod of time corresponding to a predetermined percentage of theforward stroke of the piston assembly means, means for feeding said gasfrom said primary chamber to said refrigeration heat load means and tosaid secondary chamber during at least a portion of the reverse strokeof said piston assembly means, said means for feeding gas to saidprimary chamber and said means for feeding gas from said primary chamberto said secondary chamber including common channel means formed by aregenerator having a connection for each end thereof, one of saidregenerator connections being coupled to said primary chamber, and valvemeans interposed between the other of the regenerator connections andthe source of gas and the other of the regenerator connections and thesecondary chamber for connecting said source of gas to said regeneratorduring the first period of time and said regenerator to said secondarychamber during the second period of time, and means for releasing gasfrom said secondary chamber during at least a portion of the forwardstroke.
 33. The refrigerator of claim 32 wherein said means for feedingthe gas from the primary chamber comprises means for feeding gas to saidrefrigeration heat load means during a first portion of the reversestroke and means for feeding the gas to the secondary chamber during asecond portion of the reverse stroke.
 34. The device of claim 32 whereinsaid primary gas work chamber is divided into a plurality of separatesections of different effective cross-sectional areas, said first pistonportion including a separate piston member for each of said chambersections.
 35. In a refrigerator, primary and secondary gas workchambers, piston assembly means having first and second piston portionsmounted for reciprocating motion in said primary and secondary chambersrespectively, said piston portions being connected to each other so thatwith the motion thereof, the effective volumes of said chambers arevaried in substantially inverse relationship, means for driving saidpiston portions reciprocally in said chambers, a source of gas, meansfor feeding said gas to said primary chamber during a first period oftime corresponding to a predetermined percentage of the forward strokeof the piston assembly means, means for feeding a first portion of saidgas from said primary chamber to external means to be cooled and asecond portion of said gas to said secondary chamber during at least aportion of the reverse stroke of the piston assembly means, said meansfor feeding gas to said primary chamber and said means for feeding gasfrom said primary chamber to said secondary chamber including commonchannel means formed by a regenerator having a connection for each eNdthereof, one of said regenerator connections being coupled to saidprimary chamber, and valve means interposed between the other of theregenerator connections and the source of gas and the other of theregenerator connections and the secondary chamber for connecting saidsource of gas to said regenerator during the first period of time andsaid regenerator to said secondary chamber during the second period oftime, and means for releasing gas from said secondary chamber during atleast a portion of the forward stroke.